Li-ion conductivity and crystal structure of garnet-type Li<sub>6.5</sub>La<sub>3</sub><i>M</i><sub>1.5</sub>Ta<sub>0.5</sub>O<sub>12</sub> (<i>M</i> = Hf, Sn) oxides

Abstract

We investigated the Li-ion conductivity and crystal structure of the Ta-doped Li7La3M2O12 (M = Hf, Sn) samples. All of the Ta-doped samples exhibited a relatively high conductivity of ∼10−4 S cm−1 at room temperature, and the activation energies of Li6.5La3Hf1.5Ta0.5O12 and Li6.5La3Sn1.5Ta0.5O12, which were determined from the Arrhenius plots in measured temperature range, are Ea = 0.400(6) and 0.451(1) eV, respectively. The crystal structure was analyzed by Rietveld method using powder X-ray diffraction data. From a view point of the Li–O polyhedral volume in unit cell, Li6.5La3Hf1.5Ta0.5O12 has a most suitable Li-ion environment among the Li7La3M2O12 (M = Zr, Hf, Sn) compounds.